Interleukin-7 or a polypeptide having a similar activity thereto (hereinafter, ‘IL-7’) is an immunostimulatory cytokine which can promote immune responses mediated by B cells and T cells, and in particular, IL-7 plays an important role in an adaptive immune system. IL-7 is mostly secreted by stromal cells in the bone marrow and thymus, but it is also produced by keratinocytes, dendritic cells, hepatocytes, neurons, and epithelial cells (Heufler C et al., 1993, J. Exp. Med. 178 (3): 1109-14; Kroncke R et al., 1996, Eur. J. Immunol. 26 (10): 2541-4: Sawa Y et al., 2009, Immunity 30 (3): 447-57; Watanabe M et al., 1995, J. Clin. Invest. 95 (6): 2945-53).
Specifically, IL-7 activates immune functions through the survival and differentiation of T cells and B cells, survival of lymphoid cells, stimulation of activity of natural killer (NK) cell, etc., and in particular, IL-7 is important for the development of T cells and B cells. IL-7 binds to hepatocyte growth factor (HGF) and functions as a pre-pro-B cell growth-stimulating factor and a cofactor for V(D)J rearrangement of the T cell receptor beta (TCRI3) (Muegge K, 1993, Science 261 (5117): 93-5).
Additionally, IL-7 regulates the development of lymph nodes through lymphoid tissue inducer (LTi) cells and promotes the survival and division of naive T cells or memory T cells. According to the clinical results on viral infection reported recently, IL-7 maintains naive T cells or memory T cells (Amila Patel, J Antimicrob Chemother 2010). Furthermore, IL-7 enhances immune response in human by promoting the secretion of IL-2 and interferon-γ.
That is, IL-7 is a cytokine for promoting the survival and proliferation of T cells, B cells, and other immune cells, and it is an excellent candidate material for an immune therapeutic agent which is applicable in various diseases, such as viral infection, cancer, and immune system injury. Recently, several clinical studies on malignancies and human immunodeficiency virus (HIV) infection confirmed the effect of IL-7 on increasing the immunity in human bodies (Fry T J et al., 2002, Blood 99 (11): 3892-904; Muegge K et al., 1993, Science 261 (5117): 93-5; Rosenberg S A et al., J. Immunother. 29 (3): 313-9). Additionally, IL-7 is also used for the immune recovery after the transplantation of allogenic stem cells (Snyder K M, 2006, Leuk. Lymphoma 47 (7): 1222-8) and the treatment of lymphopenia.
Cancer is life threatening disease. Cancer cells provide an environment that can inhibit immune system so that they can grow without being recognized by immune cells. Cancer patients show an immune deterioration in which T cells are reduced mainly due to anticancer treatment (e.g. chemotherapy, radio-therapy) or showed reduced number at the time of cancer diagnosed. Additionally, although cytotoxic T lymphocytes, effector T cells, and macrophages are gathered inside the cancer tissue, they cannot effectively remove cancer cells. Further, immune cells cannot effectively inhibit the proliferation of cancer cells because T regulatory cells (Treg), myeloid-derived suppression cells (MDSC), etc., which inhibit the function of immune effector cells, are present in cancer tis sue.
Under these circumstances, immune therapies are highlighted recently. Immune therapy can be used in combination with chemotherapy or radiation therapy which are currently used for cancer treatment. In particular, the utilization of IL-7 is considered as an alternative for enhancing immune functions by overcoming the lymphopenia in which the number of T cells decrease.
Chronic infection is sustained by inducing exhaustion of T cells that recognize viruses. For example, by being infected with viruses such as HIV, hepatitis B (HBV), hepatitis C (HCV) and simian immunodeficiency virus (SIV), initial immune response is strongly induced, but the functions of virus-specific T cells gradually decrease along with time. In particular, the functions of the virus-specific T cells are reduced by PD-1, LAG-3, TIM-3, IL-10 receptor, TGF-β receptor, etc.
However, IL-7 recovers the loss of functions of the virus-specific T cells or inhibits the decrease of their functions by overcoming the immune inhibitory signal system (Pellegrini M, 2009 May; 15 (5): 528-36). Further, IL-7 induces the proliferation of T cells and increases the expression of Bcl-2 thereby promoting the expansion and survival of T cells.
Additionally, IL-7 produces cytokines and helps to retain their functions by inhibiting the expression of SOCS3, which is a mediator for inhibiting cytokine signaling. Further, IL-7 reduces immunopathology due to the production of IL-22 (Som G. Nanjappa, Blood. 2011; 117 (19): 5123-5132, Marc Pellegrini, Cell 144, 601-613, Feb. 18, 2011).
However, when a recombinant IL-7 is produced for the purpose of medicinal utilization, there are problems in that impurities increase compared to the general recombinant proteins, the amount of IL-7 degradation, and large-scale production cannot be easily achieved. Previously, Cytheris Inc. has been developed a synthetic IL-7, which is a conformer having particular disulfide-bonds (Cys: 1-4; 2-5; 3-6) (U.S. Pat. No. 7,585,947). However, since production of synthetic IL-7 requires a complicated denaturation process, the manufacturing process is not easy. Accordingly, there are strong needs for developing a modified IL-7 protein which can be produced in large-scale and by an easy manufacturing process.
In this regard, the modified IL-7, which can be produced in large-scale and by an easy manufacturing process, was manufactured, thereby completing the present invention.